The goal of the research is to clarify the role of the viral genome in transformation by the small DNA tumor virus, simian virus 40 (SV40). The viral genome and viral gene expression will be studied in phenotypically normal revertants derived from and SV40 transformed mouse cell line, SVT2. The revertant cell lines contian integrated SV40 DNA but exhibit a homeostatic pattern of G1 arrest in confluent culture and are not tumorigenic. The two growth properties distinguish these revertant lines from SVT2 and also from other revertant lines previously derived from SV40 transformed mouse cells. The revertants display the nuclear SV40-specific T antigen in a growth-dependent manner; rapidly growing cells have detectable T antigen whereas quiescent cells do not. The quantity of viral DNA present, its site of integration, and its biological and physical properties will be examined in the revertants and compared to the viral genome in the parental transformed cell. The virus specific RNA and virus specific proteins present in the revertants will be quantified and characterized as a function of growth state.